Primary considerations in the design of such tanks are that they should be large enough for the water filling them to provide adequate containment for the explosive forces employed, that the structure should be able to withstand repeated applications of the explosive forces without damage, that the area adjacent the tank should be subjected to the minimum of noise and vibration, and that there be a minimum expulsion of water from the tank following an explosion.
In order to minimize the transmission of noise and vibration, designs of tank have been evolved in which the tank proper is sunk into a hole in the ground, with an air gap between the walls of the tank and the walls of the execavated hole. In order to protect the walls of the tank, the inner surfaces of the walls have been cushioned with air. In one method of producing this air cushion, both the bottom and side inner walls of the tank are lined by spiral coils of air filled hose. The substantial buoyancy of such hoses, and the considerable turbulence induced in the water by the explosions, makes it difficult to secure the coiled hose in situ against the side wall. Occasional leaks or damage to the hose are prone to occur, and any leak in the hose will disable the entire side wall protection. In another design, the side walls are protected by an annular curtain of air bubbles produced by discharging air from an annular sparge at the bottom of the tank. Although the air bubbles provide an effective cushion, a substantial air supply is required and also the air curtain tends to spread as it rises in the tank, thus reducing the effective capacity of the tank.
A further serious problem that can arise with these prior art tanks is that the application of explosive forces can cause the tank to "ring" like a bell with low frequency vibrations of high amplitude. This not only strains the tank structure but results in additional water being expelled violently upwardly from the tank. The top of the tank cannot be more than partially closed because of the necessity for allowing the explosion gases to escape.